Expandable reamers are typically employed for enlarging subterranean boreholes. Conventionally, in drilling oil, gas, and geothermal wells, casing is installed and cemented to prevent the wellbore walls from caving into the subterranean borehole while providing requisite shoring for subsequent drilling operation to achieve greater depths. Casing is also conventionally installed to isolate different formations, to prevent cross-flow of formation fluids, and to enable control of formation fluids and pressure as the borehole is drilled. To increase the depth of a previously drilled borehole, new casing is laid within and extended below the previous casing. While adding additional casing allows a borehole to reach greater depths, it has the disadvantage of narrowing the borehole. Narrowing the borehole restricts the diameter of any subsequent sections of the well because the drill bit and any further casing must pass through the existing casing. As reductions in the borehole diameter are undesirable because they limit the production flow rate of oil and gas through the borehole, it is often desirable to enlarge a subterranean borehole to provide a larger borehole diameter for installing additional casing beyond previously installed casing as well as to enable better production flow rates of hydrocarbons through the borehole.
Expandable reamers may be used to enlarge a subterranean borehole and may include blades that are pivotably or hingedly affixed to a tubular body and actuated by way of a piston or by the pressure of the drilling fluid flowing through the body. For example, U.S. Pat. No. 7,900,717 to Radford et al. discloses an expandable reamer including blades that may be expanded by introducing a fluid restricting element such as a ball into the fluid flow path through the drill string. The ball may become trapped in a portion of the reamer, thereby, causing fluid pressure to build above the ball. The fluid pressure may then be used to trigger the expandable reamer and move the blades to an extended position for reaming. Other expandable apparatus, such as an expandable stabilizer may be triggered and expanded in a similar manner. However, in such expandable apparatus, the ball may not be removed from within the expandable apparatus without removing the entire drill string form the borehole. Accordingly, in many downhole operations, an expandable apparatus, which includes a ball triggering system, may be triggered only once during the downhole operation (e.g., drilling or reaming operation).